| ??? 08/31/06 04:22 Modified: 08/31/06 04:31 Read: times Msg Score: +1 +1 Good Answer/Helpful |
#123419 - 5k trimmer is not well suited Responding to: ???'s previous message |
Mehdi said:
He used a 5k multi turn for ADC analog input, and 0.1uF,1uF multilayer and 10uF tantal for these inputs. You mean caps from inputs to ground? Which ground? Hopefully analog ground? By the way, due to the internal input resistances (see figure 3 of below datasheet) a 5k trimmer isn't well suited to apply an "identical" potential to all inputs: When the input resistances differ from channel to channel, then this also results in different voltage dividings with the 5k trimmer. Have a look at figure 4 of datasheet to see how the inputs have to be driven: http://www.analog.com/UploadedF...7862_0.pdf Take care, such a fast ADC, showing a very short aquisition time, needs a very fast and very precise Opamp at its inputs!! The OPamp must settle to less than 0.02% within the aquisition time, which is 300nsec (!) for the AD7862, otherwise the 12bit precision is eroded! Kai |
| Topic | Author | Date |
| Problem With AD7862 | 01/01/70 00:00 | |
| Reference generator | 01/01/70 00:00 | |
| Reference generator | 01/01/70 00:00 | |
| Try | 01/01/70 00:00 | |
| Thanks Steve | 01/01/70 00:00 | |
| Is this a problem? | 01/01/70 00:00 | |
| Huge Osc | 01/01/70 00:00 | |
| Picture | 01/01/70 00:00 | |
| Ok | 01/01/70 00:00 | |
| Picture | 01/01/70 00:00 | |
| Picture-Jpeg | 01/01/70 00:00 | |
| ? | 01/01/70 00:00 | |
| ? | 01/01/70 00:00 | |
| AD 7900 | 01/01/70 00:00 | |
| Its there... | 01/01/70 00:00 | |
| Sorry | 01/01/70 00:00 | |
| excuse me | 01/01/70 00:00 | |
| What oscillation without averaging? | 01/01/70 00:00 | |
| Averaging! | 01/01/70 00:00 | |
| Do you mean... | 01/01/70 00:00 | |
| No | 01/01/70 00:00 | |
| How did you measure it? | 01/01/70 00:00 | |
| 10mH chokes | 01/01/70 00:00 | |
| agnd and dgnd | 01/01/70 00:00 | |
| Highly unsuited! | 01/01/70 00:00 | |
| Lcd | 01/01/70 00:00 | |
| What do you mean? | 01/01/70 00:00 | |
| jp4 and jp5 | 01/01/70 00:00 | |
| Please explain | 01/01/70 00:00 | |
| Lcd | 01/01/70 00:00 | |
Use a scope to check it | 01/01/70 00:00 | |
| 5k trimmer is not well suited | 01/01/70 00:00 | |
| 5k trimmer is not well suited | 01/01/70 00:00 | |
| What do you mean by "huge oscillation"? | 01/01/70 00:00 | |
| changed to a new part and it doesn't work | 01/01/70 00:00 |